The interface between abiotic and biotic stress responses.

Organisms are under strong selection to respond adaptively to environmental stress, even when different stresses occur simultaneously or in rapid succession, as they often do in natural environments. However, at a molecular level, stress responses are often studied in isolation and under controlled growth conditions. This leaves us with an ever-finer picture of single stress responses but little understanding of how additional stressors modify those responses. Without companion studies of more complex systems of interacting stresses, we do not know how phenotypes are shaped under natural conditions. Based on whole organism studies in largely agricultural settings, we do know that stresses interact profoundly to shape phenotypes. We also have examples of cross-talk among signalling pathways associated with specific abiotic and biotic stress responses which hint at the existence of mechanisms that may integrate global plant stress responses. To move plant stress biology forward in transformative ways, we need greater collaboration among plant biologists studying different stresses in order to address the complexity of plant stress responses under natural conditions. In 2015, the University of Missouri Interdisciplinary Plant Group (IPG) organized its annual symposium around the topic of Plants Between a Rock and a Hard Place: The Interface between Plant Abiotic and Biotic Stress Responses. A primary goal of the meeting was to promote and enhance multi-stress collaboration within the plant stress biology community by bringing together world-renowned experts in different aspects of plant stress biology who have already begun to study the interactions between different stresses. In this special issue of the Journal of Experimental Botany, we present some of the topics and research that were covered at the symposium. Foyer et al. (2016) set the stage with a detailed look at how an abiotic stress can shape a plant's response to attack by phloem-feeding aphids. They present a strong case to challenge the oft-held notion that abiotic stress events result in an increased susceptibility to biotic stress factors. The complex signalling pathways that direct plant responses to abiotic and biotic stressors overlap in many ways that lead to cross-tolerance phenomena. The plant's response to aphid infestation involves interactions between hormone, redox, nitric oxide, kinase, and calcium signalling pathways that mirror aspects of the plant's response to abiotic factors. The preponderance of evidence suggests that abiotic stressors do not predispose a plant to aphid attack and, in fact, may provide some measure of protection and that this may hold true …